Effect of methane emission increases in East Asia on atmospheric circulation and ozone.

We used a fully coupled chemistry-climate model (version 3 of the Whole Atmosphere Community Climate Model, WACCM3) to investigate the effect of methane (CH) emission increases, especially in East Asia and North America, on atmospheric temperature, circulation and ozone (O). We show that CH emission increases strengthen westerly winds in the Northern Hemisphere midlatitudes, accelerate the Brewer-Dobson (BD) circulation, and cause an increase in the mass flux across the tropopause. However, the BD circulation in the tropics between 10°S and 10°N at 100 hPa weakens as CH emissions increase in East Asia and strengthens when CH emissions increase in North America. When CH emissions are increased by 50% in East Asia and 15% globally, the stratospheric temperature cools by up to 0.15 K, and the stratospheric O increases by 45 ppbv and 60 ppbv, respectively. A 50% increase of CH emissions in North America (with an amplitude of stratospheric O increases by 60 ppbv) has a greater influence on the stratospheric O than the same CH emissions increase in East Asia. CH emission increases in East Asia and North America reduce the concentration of tropospheric hydroxyl radicals (4% and 2%, respectively) and increase the concentration of mid-tropospheric O3 (5% and 4%, respectively) in the Northern Hemisphere midlatitudes. When CH emissions increase in East Asia, the increase in the tropospheric O concentration is largest in August. When CH emissions increase in North America, the increase in the O concentration is largest in July in the mid-troposphere, and in April in the upper troposphere. [ABSTRACT FROM AUTHOR]